Good evening all, I want to start by thanking everyone in advance. As of last weekend I am a first time sailboat owner. I bought a 1974 Pearson 26 as it appears to be a solid, stable, "beginner" boat. I wanted something big enough for my wife and three little ones. I've sailed with my father in the past but that was in the early 90's!

Anyhow, although the boat is in remarkably good shape, there are a few things I want to address and I'm trying to lineup a few projects. The first relatively large project is to refinish the deckpaint. At some point one of the PO's painted the deck and painted directly over the non skid areas. There are areas now that are flaking up revealing what I can only imagine is the original gelcoat (aqua colored.) The PO claims that it started doing this when he pressure washed the deck. I'd like to strip/sand everything and start over but my first question is, do marina's generally require you to haul out boats before sanding/refinishing or can I just do it in its slip? I'll only be touching the deck, the hull is in good shape.

Probably gelcoat had wax or other residue and not properly sanded. I use a Mirka vacuum sander and never had a problem at the dock. I never ask. Twice I had someone watch what I was doing. Look at the water and leave when satisfied I wasn't putting sanding residue in the water.
When you strip the paint, do a proper sanding and wipe down. Use a primer made for coating fiberglass. Pay attention to required temperatures and humidity.